How to use phone microphone with Bluetooth FM transmitter?

I have a car Bluetooth FM transmitter that connects to my Android phone. The problem is that the transmitter’s microphone is very bad and people can hardly hear me when I make calls or use Google Assistant. I want to use my phone’s microphone instead of the transmitter’s microphone, but still use the transmitter’s speaker. Is there any way to do that? I tried looking for a setting to choose which microphone to use, but I couldn’t find any. My transmitter model is Car FM Transmitter W 2.4A USB Charger, Nulaxy™ 2015 Newest Wireless Bluetooth FM Transmitter Car Kit for All Smartphones, Tablets, MP3 Players. Any help would be appreciated. Thanks.